Forage Fish Conservation Act of 2021 This bill addresses the management and conservation of forage fish. The Department of Commerce must issue a definition for the term forage fish . It must consider certain factors in defining such term, including whether a species covered by the definition (1) is at a low trophic level; (2) is generally small to intermediate-sized; (3) occurs in schools or other dense aggregations; (4) contributes significantly to the diets of other fish, marine mammals, or birds; and (5) serves as a conduit for energy transfer to species at a higher trophic level. Commerce must also establish guidelines to assist regional fishery management councils in (1) developing a list of unmanaged forage fish areas and prohibiting the development of any new forage fish fisheries until the potential impacts of such fisheries have been assessed; and (2) setting annual catch limits for forage fish fisheries that assess, specify, and reduce such limits by the diet needs of other fish species and marine wildlife. The bill adds shad (American shad and hickory shad) and river herring (blueback herring and alewife) to the list of managed stocks for the New England and Mid-Atlantic Fishery Management Council.